Question

24+27+30+………+111+114

Answer 1

S=3•[(1+2+3+4+…+8+9+10+…+37+38)-1-2-3-4-5-6-7]
S=3•[(38•39):2-(1+2+3+4+5+6+7)]
S=[(19•39)-(7•8):2]
S=(741-56:2)
S=3•713
S=2139

Answer 2

Explicație pas cu pas:

$24 + 27 + 30 + ... + 111 + 114 = 24 + (24 + 3) + (24 + 6) + ... + (24 + 87) + (24 + 90) = \underbrace{24 + 24 + ... + 24}_{31} + (3 + 6 + ... + 87 + 90) = 24 \cdot 31 + 3 \cdot (1 + 2 + ... + 29 + 30) = 744 + 3 \cdot \dfrac{30 \cdot 31}{2} = 744 + 1395 = \bf 2139$